(1) Field of the Invention
This invention relates to a hydrophone system that can communicate wirelessly with a receiver. More specifically the invention relates to a wireless hydrophone that produces a digitally-modulated, radio-frequency signal containing telemetry information. The invention is specifically adapted for use on vessels.
(2) Description of the Prior Art
It is desirable to have a large number of hydrophones positioned on a submarine in order to increase aperture size and provide greater detail in acoustic imaging. Under current technology, hydrophones used in sonar systems are deployed on submarines in select locations. These locations must have exposure to the aquatic environment, and the hydrophones must have a communication path to the interior of the submarine. Additionally, hydrophones must be positioned in an environment having low flow noise and engine noise. In view of these criteria, hydrophone arrays are limited in size and location.
In order to overcome these limitations, it has been proposed that sensors be incorporated outside the hull of the submarine. The use of wireless communication with these sensors acts to minimize the number of hull penetrations required to provide a communication path to the interior of the submarine. These sensors must also have limited power consumption to allow for long battery life or even the possibility of wireless power transmission. In the latter, power transmission efficiencies tend to be low, mandating the very lowest power consumption for the sensor and its associated electronics.
In the underwater environment, the need for wireless hydrophones has been accelerated by the interest in smart-skin type embedded sensors on the hulls of Navy platforms. Such sensors are placed in large numbers on the platform skin surface, and the data from those sensors may be transmitted wirelessly to receivers located inside or underlying the “skin” structure.
The prior art discloses wireless digital microphones for use in security systems and the like. These systems are not specifically adapted to underwater use. In an aquatic environment, radio waves do not carry for a significant distance unless extremely low frequency waves are used. Extremely low frequency waves do not support the high data transfer rates required for sonar systems. Hydrophones differ from microphones in that they are constructed to withstand high pressure environments under water at depth. Because of this construction, hydrophones are highly capacitive, and the output signal requires special conditioning before preamplification. Accordingly, wireless microphones are not readily adaptable to underwater use.